Background and aims Huntington's disease (HD) is a congenital neurodegenerative disorder that affects a lot of people around the world. In the U.S. the prevalence is about 5–10 people affected per 100 000 inhabitants and in Maracaibo (Venezuela) there is a high incidence. In Brazil there are no exact numbers of people with HD; there is an estimated 1000 families affected (ABH, 2005). In Feira Grande, a small city (about 22 000 inhabitants) of Alagoas northeastern Brazil, research discovered a kind of neurodegenerative disease that affected some families a lot of years ago and until 2005 it was believed to be Parkinson's disease. Then, after referral of patients for clinical, neurological biochemical and genetic evaluation (September 2005), the true diagnosis was finally obtained - HD. The aim of this work is to determine the prevalence of the population affected with HD today in Feira Grande, Brazil.

Material and methods The population, about 22 000 inhabitants, was investigated by interview and questionnaire. Some pedigrees in each family were constructed so that we could observe genetic correlations, because all the person had the same inheritance genetics. All pedigrees had correlations with each other.

Results We observed a large number of sibling marriages (between cousins). We found 22 cases of HD in Feira Grande. This means that the prevalence in this small city is about 1 in 1000 births.

Conclusion These results show the population of Feira Grande has the highest prevalence of HD in Brazil because of the large number of sibling marriages.